Antimicrobial metal ion solutions have been used as disinfectants. Silver solutions have been used as disinfectants in cooling towers, swimming pools, hot water systems in hospitals, portable water systems and spa pools. Additionally, silver ion solutions have been prepared for the treatment of wounds, however the silver ions used in the proposed methods are unstable and must be generated near the wound in order to deliver a therapeutic dose to the wound site.
Silver salts, such as silver citrate salts, have also been proposed as antimicrobial dusting agents. However, these dusting agents must be kept dry and are generally not convenient for imparting preservative value to consumer products or for delivering antimicrobial effects to an end user or to the environment of the end user. Colloidal silver has found a variety of uses, including: as a wood preservative; as a disinfectant of food and beverage containers and industrial processing equipment; as a bactericide in paints; as a biocide in synthetic polymer films; and as a sterilizing agent in bandages.
Aqueous solutions of silver dihydrogen citrate and citric acid have been disclosed in U.S. Pat. No. 6,197,814 (incorporated herein in its entirety) as disinfectants in a variety of settings. These water solutions of silver dihydrogen citrate and citric acid are made by passing an electrical current through a pair of silver electrodes that are immersed in a water solution of citric acid. These silver dihydrogen citrate solutions are effective against a wide-variety of microbes, including bacteria, viruses and fungi, and are non-toxic in the human environment at concentrations effective to combat microbial infestation. However, aqueous solutions are bulky and heavy, and are thus uneconomical to store and to transport.
There is a need for silver dihydrogen citrate compositions that can be economically stored, transported or both. Such compositions should be substantially free of water in order to minimize the space required for their storage, as well to minimize their shipping weight. Such compositions should confer the same beneficial antimicrobial effect as solutions of silver dihydrogen citrate when combined with water or other aqueous solution. The present invention satisfies this need and provides related advantages as well.